Stabilizing device



Oct. 4, 1966 .1. BERNE STABILIZING DEVICE 3 Sheets-Sheet 1 Filed Oct. 9,1964 INVENTOR JEAN BERNE ATTORNEYS Oct. 4, 1966 J. BERNE v STABILIZINGDEVICE Filed OCL. 9, 1964 5 Sheets-Sheet 2 INVENTOR JBA N BERNE BYGJ\3.A

ATTORNEYS Filed oct. 9, 1964 Oct.v 4, 1966 J. BERNE 3,276,746

STABILI Z ING DEVICE 5 Sheets-Sheet 3 INVENTOR JEAN ERA/E BfmgmuATTORNEYS United States Patent C) 3,276,746 STABILIZING DEVICE JeanBerne, Vernoullet, France, assignor to Institut Francais du Petrole, desCarburants & Lubrifiants, Rueil-Malmaison, Seine-et-Oise, France FiledOct. 9, 1964, Ser. No. 402,742 Claims priority, application France, Oct.10, 1963, 950,240 4 Claims. (Cl. 254-172) The object of this inventionis a device for stabilizing the lweight on the drill bit in the case ofunderwater drilling carried out from a boat by means of a flexible tubefrom which is suspended the bit anda bottom motor driving it.

Up to the present, underwater drilling has -generally been effected withIa rigid drill pipe string running from the ship and held fairlyvertically from the well head.

Such a system necessitates the use of a ship equipped with adrilling-machine and also has all the drawbacks inherent in the use of arigid ldrill pipe string, mainly due to the numerous pipe connectionsnecessary.

The use of a flexible tube formed by one sole length or by-very longelements 'would remedy these drawbacks, but proves to be very difficultto employ as it necessitates the use of a bottom motor (generallyelectric) which is unable to take very big load variations.

But the movement of the ship, particularly due to swell, causesincessant displacement of the unit for-med by the drilling tube, thebottom motor and the bit, and this results in considerable variations inthe weight on the bit, making it practically impossible for the latterto work.

The object of this invention is to remedy that :drawback by meansenabling the lweight on the bit to be kept substantially constantdespite pounding or other movement to which the boat, from where thedrilling is being done, may be subjected.

This can be done by rendering the tube substantially independent of theboats movement, so that the group formed by the immersed tube (which isdesignated hereinaiter by flexible tubing), the bottom motor and thedrill bit (the latter two being fixed t-o the end of the tube) remainpractically stationary when the boat is affected by swell, the soledisplacements being those caused by the progress in drilling.

This is achieved by the stabilizing device according to this invention,which comprises in combination handling means such as a caterpillardrive n said floating base, flexible tube means for drilling, supportedat one end thereof by said handling means, a jack arranged on thefloating base, means for feeding said jack by fluid under pressure, aframe supported by the piston of said jack, a slide guide fixed on thefloating base, first pulley means being carried by said frame, saidflexible tube means passing over said first pulley means, said framebeing substantially vertically movable upward and downward along saidslide guide, said slide guide carrying second pulley means, aguide-rope, and a mooring mass, substantially at the 'well heard, saidguide-rope passing over said second pulley means, having one end fixedto said mooring-mass and the other end fastened to the floating base,for instance through a winding and unwinding device such Ias a winch andmeans for guiding the guiderope length between the second pulley meansand the fastening point of the guide-rope to the floating base, wherebyonly a part of said length is movable with said frame.

According to a rst embodiment of the invention, said means for guidingthe guide-rope comprise two rollers positioned opposite each other oneither side of the guiderope, in Contact therewith and at the samedistance from said slide guide as the end of the flexible tube supportedby said handling means.

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According to a second preferred embodiment of the invention said meansfor guiding the guide-rope comprise two rollers being in contact withsaid guide-rope and being placed above and below said guide-rope,respectively, and `at `different distances relative to said slide guide,the upper roller being the farther from the slide guide and the lowerroller being the nearer to the slide guide, and the movable part of theguide-rope being limited by the upper `roller when it moves upward andby the lower roller 'when it moves downward.

In this last mentioned embodiment the upper roller is placed at such adistance from the slide guide that when the trame rises above thealignment position of the top of the second pulley means with the tworollers, the movable part of the guide-rope included between the saidpulley means and the said upper roller exceeds the movable part of theflexible tubing included between its holding point and the first pulleymeans by a length chosen so as to compensate for the shortening effectaccompanying the reduction in tension of the flexible tube meansresulting (from the rising of the frame, and the lower roller is placedat such a distance from the slide guide that when the frame drops belowthe alignment position of the second pulley means with the two rollersthe movable part of the flexible tube means included between its holdingpoint and the first pulley means exceeds the movable part of theguide-rope included between the second pulley means and the said lowerroller by la length chosen so as to compensate for the elongation effectaccompanying the increase in the guide-rope tension resulting from thelowering of the frame.

The device according to the invention will be described in greaterdetail hereinafter, reference being made to the appended drawings inwhich like reference numerals refer to like parts throughout the severalfigures and where- FIGURE 1 is an overall view of the device,

FIGURE la is a ldiagrammatic view of the device illustrated in FIG. l,

FIGURE 2 illustrates the use of correcting devices for adjusting tensionvariations on the guide-rope so as to keep the tension of the flexibletubing substantially constant when the ship is subjected to ventiealdisplacement.

FIGURES 1 and la should be referred to in connection `with theexplanation of the general operating principle of the device accordingto the invention.

A flexible drill string (tubing) 1, from which is suspended at O yanelectric drilling motor 2 operating a tool 3, passes over a reversingpulley 4 and is kept under tensi-on by a caterpillar |drive 5 used tofree, as and when required, the tubing lengths required for the drillingad- Vance.

The caterpillar drive is a standard one such as is used in cable-worksfor cable traction. It consists of two endless chains C1 and C2 withtrack-links P. These chains are placed facing each other and enclose theflexible tube 1 between their track-links. Each chain winds around twowheels R capable of revolving around a vertical spindle borne by frameK. Wheels R can be driven by cogwheels S on an axle which is turned byhorizontal endless screw V supported by a frame, the said screw beingitself driven by a motor M (FIGURE l).

Standard (e.g. hydraulic) means for compressing the two endless chainsC1 and C2 against the portion of tube they enclose can advantageously beprovided (not shown in the figure).

The flexible tube 1 is wound on a storage drum T which can be revolvedby a motor m1.

Drilling fluid is fed to the flexible tube 1 by an axial channel of thedrum connected to the end of the tube 1.

The electric conductors supplying the electric motor 2 are sunk in thecore of the flexible tube and end in collector rings on the drum axle. nthese rings collectors rub against brushes at the current source feedingmotor 2.

A guidearope 6 has its immersed end E fixed on the mooring-mass at thewell head. It passes over a reversing pulley 8 to which an upwardvertical force is applied by the piston of a jack 14, then between twoside-by-side rollers 9 and 10 before being wound by its other end on thebarrel of a winch 11, for instance. By having this Winch driven by themotor m2 it is possible to allow for the very slow variations in theheight of the boat N due to the tide. In the following, however, it willbe considered that the wound-out length of the guide-rope is adjustedperiodically and it will be assumed that tidal iniluence during the unitdrilling period is nil.

It can be seen from FIGURES 1 and la that the distance between the topsA and D of the pulleys 4 and 8 has been chosen equal t-o the distancebetween the caterpillar outlet B and the point of contact C of rollers 9and 10, the point through which the guide-rope passes.

The quadrilateral ABCD is, therefore, a parallelogram, from which itfollows that the lengths AB and CD will remain equal whatever thepounding movement of the boat. The guide-rope is kept under tension bythe upward force exerted on a frame 13 bearing the pulley 8. In thefollowing it will be assumed that the winch 11 and the caterpillar driveremain locked, i.e. that the total lengths CDE and BAO of the guide-ropeand the flexible tube remain substantially constant.

Lengths AB and CD remaining equal, lit follows that the variations inlengths DE and AO during pounding movements of the boat will besubstantially the same and, as a result of swell movements, will beexpressed merely by a displacement of a slide guide 12 (being integralwith the boat) in relation to the frame 13 sliding in the guide, thespindles of the pulleys 4 and 8 being fixed on 4the frame.

As can be seen from FIGURE la, the spot level of the pulley 4, forinstance, is not absolutely constant in relation to the sea bottom,since lengths AB and CD vary with the angle a of inclination of CD inrelation to the horizontal at C, i.e. with the extent of Ithe poundingmovement of the boat.

Actually, with length EDC remaining cons-tant, if the letter L standsfor the distance from point C to the vertical passing through the axlesof the pulleys 4 and 8 and the letter y stands for the displacement ofthe frame 13 in relation to its reference position corresponding to =0(A and D then being respectively in horizontal alignment with B and C),it can be said:

DC=\/L2 -l-y2 The maximum DC variation is therefore:

where ym represents maximum pounding.

Length EDC being constant, it follows that ED, which represents theelevation of the pulley 8 above the sea bottom, will vary by However, asthe pulley 4 is connected to the pulley 8 by the frame 13 and as ABCDforms a parallelogram, there will be no relative variation in lengthbetween the exible tubing and the guide-rope.

As an object of the invention is to maintain the weight on the toolfairly constant, an upward force F should be exerted on Ithe frame so asto keep the latter up.

This force F which, according to the invention, is supplied by a jack 14(FIGURES l and 2), must be substantially constant. In practice it wouldbe costly to use means of compression to ensure rigorous constancy ofthe pressure in the jack, and the simplest solution is to feed the jackfrom a tank of fluid under pressure (tank 15, FIGURES l and 2) such asan oleo-pneumatic accumulator of suicient capacity for the pressurevariations resulting from the piston displacement to remain moderate.

If v0 designates the volume of the tank for y=0, the force F developedby the jack, taking the volume variations as polytropic, will be:

P represents the weight of the frarne 13,

T the tension of the llexible tubing,

t the tension of the guide-rope. By equalizing the expressions of F andFv, there results:

The tension t of the guide-rope is linked with the length x of thelatter by an equation of the form:

k being the coecient of rigidity of the guide-rope and to the tensionfor the initial length x0 of the guide-rope (corresponding to y=0).

Similarly, the tension T of the flexible tubing is linked with thelength z thereof by the equation:

K being the coefficient of rigidity of the flexible tube and To itsinitial tension for the length zo, corresponding to y=0.

Elongations x-xo and z-zo of the guide-rope and the flexible tubing areequal and from their equality the following equation is derived:

Taking this Equation VI into account, Equation III then becomes:

As an example, application of this formula shows that for a weightP=3000 kg. of the frame, an initial tension (for y=0) of T0=7,000 kg. onthe flexible tubing, an initial tension (for y=0) of t0=3,000 kg. on theguide- 5, rope, i.e. for Sp=7,000|3,000i3,000=13,000 kg., and coeicientof rigidity values of K=120 kg./mm. k=80 kg./mm.

taking L=7 m. and using, in addition, a value of 'yS/vo equal to 0.05m.2/m.3, we find that the tension T on the exible tubing varies between5,800 kg. for y=|1 meter and 8,600 kg. for y=l meter.

Such a variation, of more than 2,800 kg., in the tension, of theflexible tubing, i.e. in the weight on the tool, is, in practice, toomuch in many cases.

According to t-he system of the invention, the length of guide-rope 6would be acted upon to keep the tension on. the flexible tubingconstant.

This can be effected, in practice, by -using two tension correctingrollers 16 and 17 placed at distances L2 and n L1 respectively from thevertical passing through the axle of the pulleys 4 and 8, as shown inthe diagram, FIG. 2.

According to whether a is positive o1' negative these correcting rollersmake it possible to lengthen or shorten the efrective length of theguide-rope. This results in a compensating variation in the tension onthe latter.

When the elevation y of t-he frame 13 above its reference positionincreases, the tension T on the rope decreases, since from Formula VIIit follows at once that T is a decreasing function of y.

This reduction in the tension T is accompanied by a reduction At in thetension t on the guide-rope since, according to Equation VI, T and thave variations in the same direction.

Reduction in tension At is associated with a lreduction in the length Axof this guide-rope, such that:

The correcting roller mechanism illustrated in FIGURE 2 will, in thatcase, make it possible to increase the apparent length of the guide-ropeby a length dx given by the formula:

By suitably choosing the position of correcting roller 17 (whichdetermines the length L1) one can, for a given value and, for instance,for t-he maximum value ym of y, obtain a value of dx exactly equal toAt/ k, k being the coefficient of rigidity of the guide-rope. The excessof apparent length of this rope over the corresponding length accordingto the embodiment illustrated in FIGURE 1, exactly compensates for theshortening of the rope under the effect of the reduction At in itstension.

Conversely, when y becomes negative, the force applied by the jack onthe frame 13 increases and the weight borne by the latter decreases.Tensions T and twill tend to rise, which willfincrease the length x ofthe guide-rope 6. To keep the length constant, the apparent length ofthis guiderope 6 must be reduced, which is done, according to theinvention, by means of a correcting roller 16 placed at a distance L2from the vertical passing through the axis of the pulleys 4 and 8, whichdistance L2 is so selected that for a certain deviation for instance fort-he greatest downward deviation (ym negative), the reduction in theelongation thereof under the eect of the increased tension to which itis subjected.

The consequence of compensation for variations in the length of theguide-rope is a compensation for variations in the tension on the eXibletubing.

It should be noted that this compensation is exact only for a givenpositive deviation and a given negative deviation, for example for themaximum deviations iym (y maximum in absolute value), as assumed in thefollowing computation.

As, for a zero value of y, the weight on the tool is fixed `at thedesired value, a certain variation in the weight on the tool willremain, caused by insufficient correction for y values between ym and 0and between 0 and -l-ym.

This variation in the weight on the tool is, however, considerably lessthan it `would be if there were no correcting rollers.

This is shown, for instance, by the following calculations made for thevalues below:

L=7 meters ym: i0] meter One takes pyS/V0=0.05 m.2/m3.

The force developed by the jack for )2:0 will be:

sp=3,100+3,000+2,000=8,100 kg.

Variations in the flexible rod tension (T -T 0=AT) in terms of y aredetermined from the Formula VII giving the value of T from which thevalue T 0:3,100 kg. is subtracted, i.e.:

For the values of y varying between -0.7 m. and +07 m. the followingtable is obtained:

TABLE 1 CCOO The position of the correcting rollers according to theinvention will be determined by the distances L1 and L2 such as:

( l) For y 0 m2(L1 L) lc K 2LL1 of which one deducts:

600 3.43 0.49L2 120,000 14L2 of which one deducts:

and L2l 6.125 meters.

For the values of y comprised between 0 and -i-ym and and fory Thevalues of At in these formulas being taken from Table l by the relation:

The corresponding tension on the flexible rod AT will be given by theformula:

The following table shows for different values of y the variations of Afand AT.

TAB LE 2 OOOOOO A comparative examination of Tables l and 2 above showsthat the use of correcting rollers, according to the invention, makes itpossible to reduce tension variations of the flexible tubing and,consequently, the weight variations on the tool from a maximum of 1,090kg. to a maximum of 106 kg. in the case envisaged. Adjustment of theposition of the corrector rollers in the above example, by cancellingout tension variations on the exible tubing for y=i0.7 meter, allowspounding divergences of more than 0.7 meter without increasing thedifference between the maximum and minimum values of the tension towhich the flexible tubing is subjected.

Actually, for y=-|-0.S meter, the variation in the flexible tubingtension is only +34 kg. i.e. far less than the maximum positivevariation recorded between -0.7 and |0-7 meter (+54 kg).

Similarly, for y=-0.8 meter, the variation in the flexible tubingtension is only 33 kg., which is also far less than the maximum negativevariation recorded between 0.7 and +07 meter (-52 kg.).

It can be seen, therefore, that the y value for which it is desired tocancel out the variation in tension on the flexible rtubing in relationto the nominal tension may very well be chosen slightly less than themaximum anticipated pounding value (ym).

This value of y, on which is based the adjustment of the correctingrollers, may also be selected of a different absolute value according towhether y is positive or negative.

In addition, the straight alignment line of the rollers may, if sodesired, be not horizontal, in which case the deviations iy will berepresented by the divergence between the top of the pulley on whichpasses the guiderope and the point of intersection of the straightalignment line of the correcting rollers (straight line tangent to theunder side of the upper roller and tangent to the upper side of Lthelower roller) with the vertical passing fi through the top of thepulley. The roller correcting mechanism will then yoperate in the sameway, but the nominal tension on the flexible rod will be chosen for aframe position such that the top of the pulley on which the guide-ropepasses will be in alignment with the rollers.

However, in the case already examined as an example, it can be seen thatthe value of $0.7 meter leads to maximum variations in the tension ofthe same order when y is negative as when it is positive (52 and 54 kg.,respectively). In that case, therefore, there is no need to provide faran adjustment based on diflerent absolute values of y according towhether it is positive or negative.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions, and,accordingly, it is desired to comprehend such modifications within thisinvention as may fall within the scope of the appended claims.

What is claimed is:

1. In an apparatus for underwater drilling having a tool and operatingfrom a floating base, a device for stabilizing the weight on said tool,comprising, in cornbination, handling means Ion said floating base,flexible tube means for drilling, held at one end thereof by saidhandling means, a jack arranged on the floating base, means for feedingsaid jack by fluid under pressure, a frame supported by the piston ofsaid jack, a slide guide fixed on the floating base, first pulley meansbeing carried by said frame, said flexible tube means passing over saidfirst pulley means, said frame being substantially vertically movableupward and downward, along said slide guide which slide guide carriessecond pulley means, a guide-rope, and a mooring-mass, said guide-ropepassing over said second pulley means, having one end fixed to saidmooring-mass and the other end fastened to the floating base, and meansfor guiding the guide-rope length between the second pulley means andthe fastening point of the guide-rope to the floating base, whereby onlya part of said length is movable with said frame.

2. A stabilizing device as claimed in claim 1 wherein the said means forguiding the guide-rope comprise two rollers positioned opposite eachother on either side of the guide-rope and being in contact therewith,said means for guiding the guide-rope being placed substantially at thesame distance from said slide guide as the end of the flexible tubesupported by said handling means.

3. A stabilizing device as claimed in claim 1 wherein the said means forguiding the guide-rope comprise two rollers being in contact with saidguide-rope and being placed above and below said guide-rope,respectively, and at diflerent distances relative to said slide guide,the upper roller being the farther from the slide guide and the lowerroller being the nearer to the slide guide and the movable part of theguide-rope limited by the upper roller when it moves upward and by thelower roller when it moves downward.

4. A stabilizing device as claimed in claim 3, wherein the upper rolleris placed at such a distance from the slide guide that when the framerises above the alignment position of the top of the second pulley meanswith the two rollers, the movable part of the guide-rope includedbetween the said pulley means and the said upper roller exceeds themovable part of the flexible tubing included between its holding pointand the first pulley means by a length chosen so as to compensate forthe shortening effect accompanying the reduction in tension of theflexible tube means resulting from the rising of the frame, and in whichthe lower roller is placed at such a distance from the slide guide thatwhen the frame drops below the alignment position of the second pulleymeans with the two rollers the movable part of the flexible tube meansincluded between its holding point and the first pulley means exceedsthe movable part of the guide-rope included between the second pulleymeans and the said lower roller by a length chosen so as to compensatefor the elongation effect accompanying the increase in the guide-ropeframe.

tension resulting fromv the lowering of the References Cited by theExaminer UNITED STATES PATENTS 9/1961 Cleveland 254-188 5/1963 Evans254-172 EVON C. BLUNK, Primary Examiner.

ANDRES H. NIELSEN, Examiner.

1. IN AN APPARATUS FOR UNDERWATER DRILLING HAVING A TOOL AND OPERATINGFROM A FLOATING BASE, A DEVICE FOR STABILIZING THE WEIGHT ON SAID TOOL,COMPRISING, IN COMBINATION, HANDLING MEANS ON SAID FLOATING BASE,FLEXIBLE TUBE MEANS FOR DRILLING, HELD AT ONE END THEREOF BY SAIDHANDLING MEANS, A JACK ARRANGED ON THE FLOATING BASE, MEANS FOR FEEDINGSAID JACK BY FLUID UNDER PRESSURE, A FRAME SUPPORTED BY THE PISTON OFSAID JACK, A SLIDE GUIDE FIXED ON THE FLOATING BASE, FIRST PULLEY MEANSBEING CARRIED BY SAID FRAME, SAID FLEXIBLE TUBE MEANS PASSING OVER SAIDFIRST PULLEY MEANS, SAID FRAME BEING SUBSTANTIALLY VERTICALLY MOVABLEUPWARD AND DOWNWARD, ALONG SAID SLIDE GUIDE WHICH SLIDE GUIDE CARRIESSECOND PULLEY MEANS, A GUIDE-ROPE, AND A MOORING-MASS, SAID GUIDE-ROPEPASSING OVER SAID SECOND PULLEY MEANS, HAVING ONE ENF FIXED TO SAIDMOORING-MASS AND THE OTHER END FASTENED TO THE FLOATING BASE, AND MEANSFOR GUIDING THE GUIDE-ROPE LENGTH BETWEEN THE SECOND PULLEY MEANS ANDTHE FASTENING POINT OF THE GUIDE-ROPE TO THE FLOATING BASE, WHEREBY ONLYA PART OF SAID LENGTH IS MOVABLE WITH SAID FRAME.